ACCURACY AND SPECIFICITY OF THE DINITROBENZENESULFONATE METHODS FOR AVAILABLE LYSINE IN PROTEINS

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Abstract
Specificity of the dinitrobenzenesulfonate (DNBS) method for the ɛ‐amino group of lysine was investigated using α‐ and ɛ‐formyl lysines, L‐lysine, L‐lysyllysine, L‐lysylalanine, and ribonuclease‐S‐pep‐tide. Some reactivity of DNBS with α‐amino group remained for N‐terminal lysines that decreased as the chain length of peptides increased. It is postulated from this result that reasonable values can be expected for the available lysine in proteins. The availability of lysines in casein, lysozyme, β‐lactoglobulin, acid solubilized gluten and whole egg was determined by the fluorodinitrobenzene (FDNB) method, the trinitrobenzenesulfonate (TNBS) method and the pepsin pancreatin digestion test and compared with the DNBS method. Good agreement was obtained among the values of available lysine when determined by the FDNB, TNBS, and DNBS methods. The results of the DNBS method indicated highly significant correlations with those of the FDNB and TNBS methods and the enzymatic test. However, the TNBS method suffered from significantly poorer repeatability. The DNBS method was the simplest and quickest method with reasonable accuracy.